1. Field of the Invention
The present invention relates to a washing machine, and more particularly, to an improvement in the structure of a drive unit included in a drum type washing machine.
2. Discussion of the Related Art
Generally, drum type washing machines are designed to perform a washing operation by use of a frictional force between a drum and laundry as the drum is rotated by a drive force of a motor transmitted thereto in a state wherein the laundry is received in the drum together with wash water and detergent. The above described washing operation manner has several effects of causing damage to laundry as little as possible while preventing entangling of laundry and also providing excellent washing effects by pounding and rubbing.
Now, the configuration of a conventional drum type washing machine will be described in brief with reference to FIG. 1.
Referring to FIG. 1 illustrating the configuration of the conventional drum type washing machine in longitudinal sectional view, the conventional washing machine comprises a tub 2 installed in a cabinet 1 and a drum 3 rotatably installed in the center of the tub 2.
The tub 2 is mounted, at a lower side thereof, with a motor 5a and in turn, the motor 5a is connected to a motor pulley 18 by means of a shaft.
The drum 3 is mounted, at a rear side thereof, with a drum shaft, and a drum pulley 19 is mounted on the drum shaft.
The drum pulley 19 mounted on the drum shaft and the motor pulley 18 connected to the motor 5a are connected to each other by means of a belt 20 as a power transmission element.
The cabinet 1 is provided, at a front side thereof, with a door 21, and a gasket 22 is provided between the door 21 and the tub 2.
A hanging spring 23 is mounted between an inner ceiling surface of the cabinet 1 and an outer upper surface of the tub 2 and adapted to support the tub 2. Also, a friction damper 24 is mounted between an inner bottom surface of the cabinet 1 and an outer lower surface of the tub 2 and adapted to alleviate vibration of the tub 2 caused during a dehydrating operation.
In the above described conventional washing machine, a drive force of the motor 5a is transmitted to the drum 3 by way of the motor pulley 18, the drum pulley 19, and the belt 20 connecting the motor pulley 18 and the drum pulley 19 to each other. Such an indirect power transmission manner, however, has the following problems.
Firstly, since the drive force of the motor 5a is transmitted to the drum 3 through the belt 20 wound on both the motor pulley 18 and the drum pulley 19 rather than being directly transmitted to the drum 3, there is a high potential loss of energy in the transmission course of the drive force.
Secondly, in the course of transmitting the drive force of the motor 5a to the drum 3 through the above described several elements, such as the motor pulley 18, the drum pulley 19, and the belt 20, and the like, there inevitably exists a problem of severe noise as compared to the case where the drive force is directly transmitted to the drum 3.
Thirdly, a necessity for a great number of elements for transmitting the drive force of the motor 5a to the drum 3, such as the motor pulley 18, the drum pulley 19, the belt 20, and the like, consequently, causes a complicated product assembling operation.
Fourthly, the above described great number of elements for transmitting the drive force of the motor 5a to the drum 3 may result in a proportional increase in the number of potential failure areas, and this has a problem of increasing the generation frequency of failures.
In conclusion, due to the above described power transmission manner in which the drive force of the motor 5a is indirectly transmitted to the drum 3 only by way of the motor pulley 18, the belt 20, and the drum pulley 19, the conventional drum type washing machine has problems of a high potentiality of failures and noise generation as well as excessive consumption of energy and seriously, may result in deterioration in washing performance thereof, etc.
To solve the above described problems, the applicant of the present invention has proposed to use a direct connection type motor in a drive unit of a drum type washing machine, as disclosed in Korean Patent Laid-open Publication No. 10-2001-0037607.
In the above published patent invention, there is provided a rotor frame, which is formed by pressing an iron plate and installed to transmit a rotating force of a rotor to a drum directly while performing itself the function of a back yoke having a magnetic path. It could be found that the disclosed rotor frame has a capability of solving the above described problems of the indirect power transmission manner while achieving a simplified structure.
However, forming the rotor frame by pressing the iron plate has a difficulty, due to characteristics of a press operation, to obtain a required accuracy, more particularly, concentricity, when the thickness of the iron plate exceeds a predetermined value. On the other hand, when the rotor frame is formed by use of an iron plate having a thickness less than the predetermined value, there is a problem in that the rotor frame cannot obtain a required strength and may fluctuate during rotation.
Furthermore, to provide a passage of magnetic flux, that is to say, a magnetic path for the flow of magnetic flux generated by electric current flowing through coils of a stator, it is essential to provide a back yoke, which is made of a magnetic material and has an appropriate thickness, behind a magnet. Here, it is noted that the thinner the thickness of the back yoke, the lower a saturation point of the magnetic flux. Accordingly, when the rotor frame serving as the back yoke has a small thickness, there is a limit to increase the output of a motor even if the amount of current is increased to obtain a strong output.
Consequently, the attempt to form the rotor frame having the function of the back yoke by use of the iron plate in views of diversification of products reaches a limit due to the above described thickness problem of the rotor frame.
Also, due to characteristics of the iron plate, there is a risk in that the rotor frame tends to gather rust on its surface easily. The rust may cause deterioration in the strength of the rotor frame and in the worst case, there is a risk in that rust powder that falls from the rotor frame is attached in an air gap between the magnet and the stator, thereby acting to restrict rotation of the rotor.
In addition, the rotor frame, made of the iron plate, has a difficulty in the implementation of any subsequent process for improving accuracy and other processes.